The invention relates to a method and a device for flame monitoring.
A method and a device of the type mentioned at the start is known for example from EP 617 234 910 A1. This publication discloses an ionization flame detector with a capacitor, which is connected to a reference voltage source and via a coupling element to the secondary circuit of a firing circuit. For as long as there is no flame present between the firing electrode and the ground lead the capacitor is charged via a resistor to an operating voltage. As soon as an ionization stream flows as a result of flame generation the capacitor is discharged. The capacitor is connected to a monitoring circuit which, if a predetermined threshold value is exceeded, creates an output signal which indicates the presence of a flame.
EP 1 256 763 A2 discloses a flame monitoring method, in which the radiation created by the flame is recorded by a photoresistor and the sensor signal is evaluated on two channels. The first channel is used to record the average brightness and the second channel is used to record changing components which emanate from flickering of the flame. The flame is only recognized as burning correctly if the signal is within a predetermined range in each case at both channel outputs.